Hallock, a cocktail waitress, was last heard from by her sister-in-law on December 18, 1969 in their hometown of Fort Lauderdale, Florida. Hallock called her sister-in-law and told her that she had an appointment with a male teacher from the local junior college that evening. Hallock said that the unidentified teacher also did undercover work for the government and that the meeting revolved around a possible employment opportunity for her, which would include international travel and a high salary. She purchased a pair of black patent-leather pumps and told her sister-in-law she planned to wear the shoes that evening, along with a black cocktail dress. Hallock was never seen again.

Hallock's sister-in-law became concerned when she was unable to contact Hallock by Christmas Day, 1969. She checked Hallock's apartment shortly thereafter and discovered that Hallock's car keys, driver's license and vehicle registration were missing. Her bathtub was full and her dog had not been fed. Her sister-in-law could not locate the high heels or the black dress Hallock intended to wear to her meeting with the unidentified teacher in the apartment. Hallock's car was found abandoned in a nearby parking lot a few days later; there was no sign of her at the scene.

A missing person's report was filed for Hallock, but there was no trace of her until April 1973, over four years after her disappearance. Two gold-filled teeth and a shamrock pin discovered in the possession of Gerard John Schaefer Jr., a former Florida law enforcement officer, were identified as belonging to Hallock at that time.

Schaefer was eventually convicted of the murders of two young women in the Florida area in the 1970's and sentenced to two life prison sentences. A photo of Schaefer is posted below this case summary. Neither of the victims was Hallock; the rest of her remains have yet to be discovered, and as such she is still listed as a missing person. Schaefer is believed to be responsible for attacks, murders and disappearances of many other young women in the 1960s and 1970s.

It has been established that Schaefer was employed as an intern teacher in 1969 in Fort Lauderdale, which made him a viable candidate for suspicion in Hallock's disappearance. He also wrote a fantasy story about a woman who wore black high heels and a black dress. Schaefer claimed he penned the fantasy in 1967, two years before Hallock vanished, but authorities believe he authored the story as a reminder of his crime in 1969. Schaefer was never charged in connection with Hallock's case, although her teeth were discovered among his belongings. Possessions of other probable victims of Schaefer's, including Leigh Hainline Bonadies, were also located in his belongings at the time of his 1970's arrest. Bonadies disappeared in 1969 and her body was found in 1978, but not identified until 2004. He is also considered a suspect in the disappearances of
Peggy Rahn,
Wendy Stevenson,
Nancy Leichner and
Pamela Nater. The family of
Debora Lowe, who disappeared in 1972, believes he was involved in her case as well. All of the women are still missing.

Schaefer wrote a book with the assistance of his former girlfriend, Sondra London, entitled Killer Fiction. He was killed in prison in 1995 by another inmate, Vincent Faustino Rivera, who has since been convicted of Schaefer's murder. Florida authorities had reopened the investigations into Hallock and Bonadies' disappearances and presumed deaths in 1995, hoping to connect Schaefer to the crimes and close the cases. His murder halted any further investigation into the disappearances. Hallock has never been located and her case remains unsolved but inactive.